Halide IonsOxford AQA IGCSE Chemistry: Revision notes
Section 1
What is the test for halide ions?
Halide ions (chloride, bromide and iodide) in solution can be identified using silver nitrate solution, in the presence of dilute nitric acid. Each halide ion produces a different coloured precipitate with silver ions.
Key termshalide ionssilver nitrate solution
Section 2
How is the test carried out?
- Add a few drops of dilute nitric acid to the unknown solution (this removes other ions, such as carbonate, that could give a false-positive precipitate).
- Add a few drops of silver nitrate solution.
- Observe the colour of any precipitate formed.
Key termsdilute nitric acid
Exam tip
Always mention the dilute nitric acid step — leaving it out is a common way to lose a mark, since it is needed to rule out false positives.
Section 3
What colour precipitate does each halide ion give?
| Halide ion | Silver salt formed | Precipitate colour |
|---|---|---|
| Chloride | Silver chloride | White |
| Bromide | Silver bromide | Cream |
| Iodide | Silver iodide | Yellow |
These three colours (white, cream, yellow) are distinct enough to identify which halide ion is present in an unknown solution.
Key termssilver chloridesilver bromidesilver iodide
Common mistake
White and cream can look similar. If uncertain, note that silver chloride is a purer white, while silver bromide has a slight cream/off-white tinge.
Must Know
- Test for halide ions: add dilute nitric acid, then silver nitrate solution
- Chloride ions give a white precipitate (silver chloride)
- Bromide ions give a cream precipitate (silver bromide)
- Iodide ions give a yellow precipitate (silver iodide)
- Dilute nitric acid is added first to prevent false-positive precipitates from other ions
That's the notes covered.
Carry on to the next subtopic.